The skeletal system is composed of bones, cartilage, ligaments, and tendons that work together to provide structure and support. The major organs and tissues include the bones themselves—206 in adults—which serve as the framework; cartilage, a flexible connective tissue found at joint surfaces and in structures like the ears and nose; ligaments, which connect bones to each other and stabilize joints; and tendons, which attach muscles to bones enabling movement. Additionally, bone marrow housed within bones produces blood cells and immune cells, making it a vital component. The joints, where bones meet, allow for movement and flexibility. Some classifications also include the vertebral column (spine), skull, ribcage, and pelvis as major structural units. The skeletal system works alongside muscles in the musculoskeletal system to enable movement, protect vital organs like the heart and brain, produce blood cells, store minerals such as calcium and phosphorus, and maintain overall body structure and posture.